Scintillator members are used in various radiation measuring devices including surface contamination measuring instruments, body surface monitors, and so on. When excited by radiation, a scintillator member emits light, which is then directed onto a light receiving surface of a photomultiplier tube (PMT). In order to detect the light generated in the scintillator member with a high degree of sensitivity, a light shielding structure or a light tight structure (a dark room) for shielding the scintillator member from external light is provided on both the front and rear of the scintillator member.
With regard to light shielding on the front surface side of a scintillator member (the surface on which radiation is incident), attenuation of radiation passing through this surface should be considered. In particular, as the ability of α rays and low-energy β rays to penetrate a substance is small, a light tight film having a certain thickness would, if provided on the front surface side of a scintillator member, would make blockage and attenuation of the α and β rays reaching that surface non-negligible, and therefore considerably lower the measuring sensitivity. Thus, any light tight film provided on the front surface side of a scintillator member must be very thin. However, such thin light tight films have very low physical strength and easily become damaged or corrode. If such a thin film is damaged, scratched or has pinholes formed by scratching, light could enter through opening such as pinholes or scratch marks, making it impossible to detect weak light emission generated in the scintillator member.
In order to overcome the above problems, a technique of providing a plurality of thin light tight films such that they are spaced from each other on a front surface side of a scintillator member may be considered, as described in JP 2001-141831 A and JP 3-231187 A. Each of these light tight films includes a resin film and light tight layers formed on both sides of the resin film. With this structure, even if a light tight layer formed on the top surface of a light tight film provided on the outermost side is damaged, light can be blocked by a light tight layer formed on the rear surface side. Further, even if the entire light tight film provided on the outer side is damaged by a large external force, light shielding can be secured by an adjacent light tight film which is spaced from the damaged light tight film. While a protective grille having a lattice shape may be provided on the front surface side of the outermost light tight film as required, there is a possibility that foreign matter or a contaminant may enter through any of the openings of the lattice. On the other hand, if the area of each opening of the protective grille is reduced to thereby enhance the physical protection, the sensitivity for radiation detection would be decreased.
When a light tight film is mounted on a radiation measuring device, it is necessary to dispose the light tight film while stretching the entire film evenly, so as to prevent wrinkling of the film. This task requires technical skill and takes an immense amount of time and labor. Further, the light tight film can easily tear if excessive force is applied during the placement operation. Conventionally, these problems are very significant because, in general, multiple light tight films are mounted on each radiation measuring device.
JP 7-35869 A discloses one example radiation measuring device in which a scintillator member is used. JP 8-248139 A describes that a light tight film is attached onto a thin light emitting plate having a large area (see paragraph 0041 and so on). Neither reference, however, describes details of the light tight film or a method of attaching the light tight film. In particular, while it is necessary to dispose an extremely thin light tight film in the case of detection of α particles and low-energy β particles, no treating method specific to such a thin film is disclosed in any of the references.
JP 62-16486 U describes that a light tight film is provided on a top surface of a plastic scintillator. The light tight film includes a plastic film in a thin film shape and a deposition layer also in a thin film shape which is formed on a rear or top surface of the plastic film. This reference, however, does not describe how the light tight film in a thin film shape is provided on the plastic scintillator. JP 5-297145 A describes that a scintillator layer and a light tight layer are closely attached. However, the light tight layer is removable and is not fixedly adhered to the scintillator layer.
JP 2007-147581 A (and corresponding US2006/0151706A1) discloses a technology of adhering a film which has been removed from a thermal transfer sheet onto a light emitting plate. The film includes a protective layer, a light tight layer, an adhesion layer, and so on. This document, however, does not describe a film for transfer, which is provided with a light emitting function (i.e. a radiation detection function).